With no new challengers arising to take on the Japanese automobile manufacturer and its British driver for the title of fastest lap in a car around the Isle of Man TT circuit, Subaru and Mark Higgins had no choice but to once again break their own record. Instead of running a mostly stock car, though, Subaru provided Prodrive with a 2015 WRX STI and worked with the motorsports company to create the ultimate car for racing around the island. The end result is a more powerful, lighter, and quicker STI that’s been christened the Isle of Man TT Challenge 3 WRX STI.
Body
Made mostly of steel, Subaru’s Challenge 3 WRX STI weighs less than 2600 pounds. The interior is stripped of almost all amenities, and weight also was minimized by using fiberglass for the car’s bumpers and front fenders.
Wheels
Manufactured by Speedline, Subaru notes that the Challenge 3 WRX STI’s wheels are specially designed for this car, and are wrapped in 18-by-9-inch tires. Prodrive and Subaru had to extend the car’s already-flared fenders to ensure the wheels didn’t rub. Peeking out from behind the wheels are 14-inch, six-piston disc brakes.
Handbrake
Like a rally car, the Challenge 3 WRX STI has a massive handbrake poking up from its center console. While the lever remains untouched for the majority of the course, Higgins admits he uses it to help steer the car on through one extra-sharp corner of the Isle of Man TT circuit.
Suspension
To handle the course’s undulating public roads, the Challenge 3 WRX STI uses four-way adjustable dampers as well as a number of other suspension components derived from those used on Subaru WRC cars. Prodrive engineers compared the setup to those used by vehicles competing in the Irish Rally Tarmac Championship series.
Engine
The 2.0-liter turbocharged flat-four engine, from a Subaru WRC car, is tuned for high-end power. Thanks to Prodrive’s ministrations, the Challenge 3 WRX STI makes 600 horsepower and a little more than 590 lb-ft of torque, the latter of which is available from 4250 rpm to 8500 rpm.
Turbocharger
Made by Garrett, the Challenge 3 WRX STI’s turbocharger works with a top-mounted intercooler to keep things cool during the circuit’s long, high-rpm straights. While the wet-sump engine’s redline is currently set at 8500 rpm, Prodrive engineers believe it can be reliably revved up to 9100 rpm.
Engine Gaskets
While you wouldn’t know it from the sound, Prodrive engineers revealed that the engine doesn’t use head gaskets but Wills Rings. The metallic seals allow Prodrive engineers to have a better read on the turbocharger’s effects on cylinder-head lift, allowing them to save the engine by limiting the turbocharger’s boost if head lift becomes apparent.
Transmission
Developed by Prodrive and Xtrac, the Challenge 3 WRX STI’s six-speed manual transmission is controlled via a single paddle shifter located on the right side of the steering column. When the transmission is properly warmed up, Prodrive claims that shifts happen in less than 25 milliseconds. Should the paddle break midway through a run, the transmission will default to an automatic mode, in which case it will automatically upshift at 7500 rpm and downshift at 3500 rpm.
Packaging
In order to aid weight distribution, both the powertrain and driver are moved further back within the car’s chassis. The net result is a reported weight distribution of 52 percent front and 48 percent rear with Higgins on board.
Drag Reduction System (DRS)
Like a Formula 1 car, the Challenge 3 WRX STI is equipped with a drag reduction system (DRS), which adjusts the angle of the rear wing to help the car achieve higher speeds. Although control of DRS is via a button mounted on the steering wheel, Prodrive engineers can intervene and limit or override the system’s use if necessary.
Rear Wing
When engaged, the DRS can bring the wing up and down in as little as 40 milliseconds, thanks to a large, trunk-mounted compressor. Prodrive estimates that the entire system, wing included, contributes approximately 22 pounds to the car’s weight.
Carbon Fiber, Aluminum—and Wood
While the Challenge 3 WRX STI’s adjustable rear wing is made of carbon fiber, very few other items on the car are. In fact, the rear wing’s decorative end pieces are made of aluminum, while the front-mounted splitter is carved from wood.
Rear Differential Cooler
Due to its close proximity to the exhaust, the Challenge 3 WRX STI’s rear differential needs to be kept cool. In order to achieve this, Subaru and Prodrive cut a hole in the vehicle’s body just above the rear differential. A small fan was then installed to channel cooler air to the car’s hot rear end. Unlike your typical Subaru’s all-wheel drive system, which moves torque fore and aft as needed, the Challenge 3 WRX STI features a fixed 50/50 spilt between the front and rear axles.
Decals
A roof-mounted map of the Isle of Man TT course is one of many decals stuck onto the body of the Challenge 3 WRX STI. According to Prodrive engineers, the same individuals who apply the decals to the Mercedes AMG Petronas team’s F1 cars installed almost all of the Challenge 3 WRX STI decals.
ECU
Despite being a single-seat racecar, the Challenge 3 WRX STI’s rally roots show in its driver-side ECU placement, a common spot to place components in rally cars due to the weight offset provided by the co-driver. Most single-seat racecars place these electronics on the passenger side of the car in order to assist in counter-balancing the weight of the driver.
from Car and Driver Blog http://ift.tt/1XSbQwk
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